This invention relates to a method of manufacturing a magnetic recording medium by vacuum-depositing a magnetic film on a tape-shaped support, such as a polymer product which is being moved.
Heretofore, a coated type magnetic recording medium has been extensively employed in the prior art. It is manufactured as follows: a magnetic paint is prepared by dispersing a magnetic powder such as an oxide magnetic powder of .gamma.-Fe.sub.2 O.sub.3, .gamma.-Fe.sub.2 O.sub.3 doped with Co, Fe.sub.3 O.sub.4, Fe.sub.3 O.sub.4 doped with Co, a berthollide compound of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, a berthollide compound doped with Co or CrO.sub.2, or a ferromagnetic alloy powder essentially containing a transition metal of Co, Ni or Fe in an organic binder of vinyl chloride-vinyl acetate copolymer, stylene-butadiene copolymer, epoxy resin, or polyurethane resin. The magnetic paint thus prepared is applied to a nonmagnetic support, orientated and dried, to form a magnetic layer thereon.
Recently there has been a strong demand for high density recording data. This has led to development of "metal film" type magnetic recording media in which no organic binder is used, and in which the magnetic recording layer is a ferromagnetic metal film which is formed by a vapor deposition method such as a vacuum deposition method, a sputtering method, an ion plating method, or a plating method such as an electroplating method or an electroless deposition. Such metal film type magnetic recording media have become widely used.
In the conventional coated type magnetic recording medium, a metal oxide having a small saturation magnetization is used as the magnetic material, and the volume of the magnetic material content of the magnetic layer is only 30 to 50%. Accordingly, employment of the recording medium as a high-output, high-density recording medium is limited. Furthermore, the conventional recording medium is disadvantageous in that the manufacturing process is intricate and large auxiliary equipment is required in order to recover solvents or to prevent pollution.
The metal film type magnetic recording medium is advantageous in that ferromagnetic metal, higher in saturation magnetization than oxide magnetic material, can be provided in the form of a film without using a non-magnetic material such as an organic binder. For recording data with high density, the gap of recording and reproducing magnetic heads has been reduced to less than 1.0 .mu.m. Accordingly, the tendency has been to reduce the recording depth of the magnetic recording layer. Thus, the metal film type magnetic recording medium in which the entire thickness of the magnetic film can be used for recording magnetic signals is excellent as a high-output, high-density recording medium. Especially advantageous is an oblique incidence vacuum deposition recording medium, in which vacuum deposition is carried out by obliquely applying a ferromagnetic material vapor beam to the surface of a support. Such a deposition technique uses a relatively simple procedure, equipment and mechanism, and the resulting films have excellent magnetic characteristics.
In a conventional pblique incidence vacuum deposition method, the vapor of ferromagnetic material from a ferromagnetic material evaporating source is applied at a predetermined incident angle or with a range of incidence angles to a tape-shaped support which is moved along the cylindrical wall of a cooling rotary cylinder can.
FIG. 1 shows the essential components of a magnetic recording medium manufacturing apparatus for practicing the conventional oblique incidence vacuum deposition method. A cooling rotary cylinder can 11 is disposed in a vacuum chamber (not shown) which is evacuated by suitable vacuum pumps (not shown). As the can 11 rotates, a tape-shaped support 12 supplied from a supply roll (not shown) is conveyed along the cylindrical wall of the can 11. A ferromagnetic material evaporating source 13 is provided below the can 11, so that the vapor beam of ferromagnetic material from the source 13 is applied to the moving tape-shaped support 12 in the region which is not covered by an oblique mask 15 provided under the can 11. Thus, the vapor beam of the ferromagnetic material is applied to the tape-shaped support 12 within a certain range of incident angles, with the surface of the support 12 within the angle .alpha. being vacuum-deposited with ferromagnetic material. In this operation, only the vapor beam 14 spreading with an angle .alpha. reaches the tape-shaped support 12.
However, in the above-described conventional apparatus, the ratio of the amount of ferromagnetic material reaching the tape-shaped support from the evaporating source to the amount of ferromagnetic material provided by the evaporating source, i.e., the efficiency of vacuum deposition, is low, which makes it difficult to utilize the conventional apparatus in the industrial field.